Circuit interrupters



Nov. 25, 1969 w. LAAKSO 3,480,399

7 CIRCUIT INTERRUPTERS Filed March 18, 1968 I 2 Sheets-Sheet INVENTOR.

WILLIAM L'AAKSO W11 raw;

ATTORNEY Nov. 25, 1969 w. LAAK-SO I I 3,430,399

CIRCUIT-INTERRUPTERS Filed March 18 1968 2 Sheets-Sheet l l 54 I 40 i807 INVENTOR.

' v "WILLIAM LAAKSO 7O 1' ATTORNEY United States Patent 3,480,899CIRCUIT INTERRUPTERS William Laakso, Burnaby, British Columbia, Canada,as-

siguor to Federal Pacific Electric Company, a corporation of DelawareFiled Mar. 18, 1968, Ser. No. 713,659 Int. Cl. Htilh 85/30 US. Cl. 3376Claims ABSTRACT OF THE DISCLOSURE A circuit breaker with a fuse mountedin series with each of the separable contacts. A responder is providedwhich is responsive to the operative condition of the fuses and whichfunctions to trip and lock the circuit breaker open upon the operationof one of the fuses. The responder gives protection against singlephasing and also provides a visual indication at the front of thebreaker of the operation of the remotely mounted fuses.

This invention relates to circuit interrupters and more particularly tocircuit interrupters of the type comprising a circuit breaker having anovercurrent trip mechanism for interrupting sustained overloads andfusible members electrically connected in series with the circuitbreaker for interrupting fault currents which exceed the interruptingcapacity of the circuit breaker.

Increased use of electrical power has required larger and larger currenthandling capacity and has produced an increase in the short-circuitcurrent available. Secondary feeder circuit breakers at a distributionpoint are normally called upon to carry relatively low currents ascompared to the available short-circuit current. Unless certainprecautions are taken the short-circuit current may considerably exceedthe interrupting capacity of an otherwise suitable circuit breaker. Ausual precaution is the provision of a circuit breaker having itsovercurrent trips set for the normal current expected on the secondaryfeeder and having an interrupting rating suflicient to withstand theavailable short-circuit current. This is an uneconomic arrangementsince, in a typical installation, the breaker may have a normal ratingof perhaps 400 to 600 a. and the available short circuit current may bein the neighborhood of or in excess of 100,000 a. Breakers of the typenormally employed for 600 a. 600 v. service with a 50,000 a.interrupting capacity are considerably less expensive and take upconsiderably less room than a like unit capable of interrupting 100,000a. While over loads within the interruption rating of the low ratedbreaker could be safely handled there are those circumstances where thecircuit breaker might be called upon to interrupt a short circuitcurrent in excess of its rated capacity. It is quite possible that thelow-rated breaker would fail to clear the fault and would also bedestroyed in the process.

Current limiting fuses have been widely used because of their highinterrupting ratings. The fuses have been bolted directly to the busses,being used as power takeoff points and they have been used inconjunction with molded case circuit breakers having integral fusecompartments. The current limiting fuse, when used with such a breakeris normally provided with a striker pin. The pin is caused to trip thecircuit breaker upon the operation of the fuse, i.e., when the fuseinterrupts a short circuit. However, there are many installations wheresuch circuit breakers are not suitable.

lit has, therefore, been necessary particularly in metal cladswitchgear, to utilize circuit breakers having high fault currentinterrupting capacity. The space, size and complexity of the circuitbreakers have increased in acp CC cordance with the increasedinterrupting capacity required. As may be expected, the circuit breakersare very infrequently called upon to interrupt a major fault current andtherefore the excess expenditures were burdensome. The use ofcurrent-limiting fuses alone had been suggested for such installationsto interrupt the major fault currents. However, in order to provideproper protection for the secondary feeders it was necessary to usefuses having a fairly low overload current rating. This low ratingresulted in nuisance tripping when minor overloads occurred and requiredthe replacement of such fuses each time such a fault occurred. Thecircuit breaker elements on the other hand did not need to be replacedwhen the breaker tripped due to an overload as compared to fuses.However, fuses are particularly advantageous in their ability tointerrupt high fault current. It is an object of this invention toprovide a circuit interrupter which combines the advantages of circuitbreaker protection for moderate overloads with the advanatgeousapplication of fuses for high fault current interruption. It is anotherobject of this invention to provide a novel circuit breaker particularlysuitable for high current interruption with particularly economicapparatus.

Problems have been encountered where fuses have been employed togetherwith circuit breakers. It is particularly desirable that the fuses openonly on major fault current and that the circuit breaker contactsinterrupt only moderate overloads. This is achieved in practice byclosely coordinating the fuse normal current rating and the overcurrenttrip setting of the circuit breaker overcurrent sensing means. Thenormal fuse current rating is usually considerably in excess of thecircuit breaker trip point to insure that the fuse will not blow onminor overloads. Most major faults on secondary feeders arephase-to-ground rather than phase-to-phase. Under such circumstances itis possible that only one fuse in a multiphase interrupter will open orblow while the other fuses are not affected. Where only one phase isopened equipment connected between the other two phases will singlephase and continue to operate in most circumstances. However, thisresults in severe increases in the heating and the like of the connectedapparatus. Single phasing of three phase motors can be extremely harmfulto the motor if it should continue for any appreciable time. It istherefore an object of this invention to provide singlephase preventionin a multi-phase circuit interrupter equipped with current-limitingfuses.

In multi-phase circuit interrupters it is particularly important thatthe circuit interrupter prevent single-phasing. If an attempt is made tore-energize the circuit interrupter after one phase fuse has blown witheither the blown fuse still present or with the fuse removed, theinterrupter must immediately trip open the circuit. Most advantageouslythe circuit interrupter will remain open, i.e., with the circuit breakerin the tripped position upon blowing of any one of the associated fuses.It is therefore an object of this invention to provide an improvedcircuit breaker which is prevented from reclosing with a fuse blown orabsent.

Briefly, in the illustrative embodiment of the invention described indetail below there is shown a circuit breaker that has multiple pairs ofseparable contacts, common operating mechanism and plural overcurrentrelays; one of the relays being connected in series with each of thepairs of separable contacts. Additionally a fuse is mounted on thebreaker in series with each of the pairs of separable contacts. Aresponder is provided which is responsive to the operative condition ofthe fuses and which functions to trip and lock the circuit breaker openupon the operation of one of the fuses. The responder gives protectionagainst single phasing and also provides a visual indication at thefront of the breaker of the operation of the remotely mounted fuses.

The above and other objects and advantages of the invcntion will be bestunderstood from the following decription taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a side elevation in partial cross-section of the circuitbreaker with some parts in section and other parts omitted in theinterest of clarity;

FIG. 2 is a view taken along the line 22 of FIG. 1;

FIG. 3 is an end view taken in the direction of the arrows 3 in FIG. 2;

FIG. 4 is a vertical view corresponding to FIG. 1 showing the positionassumed by the indicator and latch upon operation of the fuse;

FIG. 5 is an end view taken in direction of the arrows 5 in FIG. 4; and

FIG. 6 is a schematic wiring diagram of the illustrative embodiment.

Referring to the drawings, the circuit breaker is of the type shown anddescribed in detail in US. Patent No. 2,833,886. It will be understoodby those skilled in the art that such circuit breakers may include one,two or three poles depending on the manner in which they are employed.The drawing of FIG. 1 is a synthesis insofar as it shows a portion ofthe operating mechanism found at the center pole in a multi-pole circuitbreaker together with other equipments normally found in the outboardpoles. The circuit breaker 10 includes a rear insulating wall 12 and ahousing or cover 14 shown in partial section. Circuit breaker 10includes a pair of movable support members 16 pivoted on fixed shaft 18.Support members 16 carry a spring loaded bridging contact block 20 onwhich are mounted the main moving contacts 22, 24 and the moving arcingand secondary contact assembly 26. Arcing contact assembly 26 isconnected by flexible braid 28 to a bus bar like member 30 that extendsalong and is secured to the wall '12. One of the main stationary contactmembers 32 is afiixed to one end of bar 30 and an overcurrent relay 34is series connected to the other. At the opposite side of the wall 12,adjacent the relay 34, a fuse connector 36 is provided for engagementwith one terminal 38 of fuse 40. Fuses 40 herein contemplated are of thewell-known current-limting type having interrupting capacities in excessof 100,000 a. The second terminal 42 of fuse 40 is connected to fuseconnector 44 which forms part of rearwardly extending contact member 46for engagement by suitable load-connected contact members, not shown,within the cubicle, not shown.

The circuit breaker is closed by an operating mechanism 47 whose detailsare unnecessary for an understanding of the present invention. Referencemay be made to US. Patent No. 2,833,886 for such details. When thecircuit breaker 10 is in its closed circuit condition as shown in FIG. 1the bridging contact 20 engages stationary contact 32 on bus 30 and asecond stationary contact 48 on conductor structure 50 that also mountsthe stationary arcing and secondary contacts 52. An arc chute, notshown, is normally positioned about the arcing contact structure. Amember 54, connected to conductor structure 50, rearwardly extendsthrough wall 12 for engagement by suitable contact members, not shown,in the cubicle, not shown.

The moving contact structures are held in the closed circuit position ofFIG. 1 against the force of the contact springs located within thesupport members 16 and auxiliary pushoff springs, not shown, by a togglemechanism indicated generally at 56. Details of the mechanism may befound in the aforementioned Patent 2,833,886. Toggle 56 is maintained inits Slightly over-centered position by a stop 58 formed as a part of thecircuit breaker frame. A latch prop 60 is carried by a multi-pole tripbar 62 pivotally supported by the circuit breaker frame. The trip barextends to each of the poles of the circuit breaker where it may beengaged by the plunger 64 of the overcurrent relay 34 to providetripping of the breaker upon prolonged overloads or overloads within theinterrupting capability of the circuit breaker. For severe overloads thefuses 40, which have a coordinated faster response time, are called uponto limit the current and to interrupt the circuit thereby preventingdamage to the circuit breaker 10.

Phase-to-ground faults are the most often encountered types wherein onephase is short circuited to ground. While opening the fuse on theeffected phase will interrupt the short circuit current it presents yetanother serious problem i.e., single phasing. Serious damage can occurto three phase motors if one phase is disconnected while the othersremain energized. While several schemes have been proposed forpreventing single phasing they have failed to achieve widespreadacceptance due to either excessive cost or complexity. Examples of thisare the utilization of striker pin equipped fuses and associated complexinterlocks.

The illustrative embodiment of the invention provides an improved meansfor avoiding single phasing and also allows remote mounting of thecurrent limiting fuses.

Referring to the drawings, the fuse condition responsive means orresponder 70 is shown mounted on a wall 72 that extends toward the cover14 from the rear wall 12 of the circuit breaker. Responder 70 includessolenoid devices 74, 76 and 78 each connected in parallel with arespective one of the fuses as shown in FIG. 6. As an example solenoid78 is connected tothe ends of fuse 40 by conductors 80, 82. Each of thesolenoids 74, 76 and 78 is identical and operates in a like manner whenenergized. Each solenoid has an armature 80, 82, 84 for driving one ofthree indicator-actuator bars 8-6, 88, 90, carried by bracket 92, to atrip indicating position. The bars are slidably supported adjacent oneend on a roll pin 94 and at the other end by an edge 96 of an aperture98 formed in the cover 14. It will be noted that the bars are notched atnear the coversupported end for purposes to be presently described. Bellcranks 100, 102 and 104 are interposed between their respectivearmatures and indicator-actuator bars. Movement of an armature istranslated into longitudinal movement of the corresponding bar by virtueof projections as for example 105 as seen in FIG. 3. The bell cranks,which are pivoted on brackets 106 by pins 108, engage the projectionsthat are formed at intervals along the bars 86, 88, 90. Theseprojections also serve as spacers to maintain separation of the bars.Pins 108 are normally below the bottom edge of the indicator-actuatorbars when the ends 86a, 88a, 90a of the bars etc., are in position onthe edge 96 of the aperture 98 in the front cover 14. Theindicator-actuator bars are resiliently retained in position by amulti-finger leaf spring 110 mounted on bracket 92 in position forengagement with notches 86b, 88b, 90b, etc., in the respectiveindicatoractuator bars. Each of the bars has a portion 860, 88c, 900 forengagement with an extension 62b of the multipole trip bar 62.

In order to best understand the invention a cycle of operation will nowbe described starting with the circuit breaker closed and energized. Inthe event of a short circuit of sutficient magnitude as to cause theoperation of respective one of the fuses, the responder 70 functions asfollows: A solenoid device, for example 74, connected parallel with theblown fuse is energized when the fuse opens. This causes the armature 80to move upward to strike bell crank 100 causing the bell crank to shiftthe indicator-actuator bar 86 laterally so that portion 86c engages thetrip bar extension 62b causing rotation of the trip bar. The rotation ofthe trip bar causes unlatchirig of the circuit breaker by removing thelatch prop 60 allowing the toggle 56 to collapse and thereby preventssingle phasing. The longitudinal movement of the bar 86 causes the end86a of the bar to drop off the edge 96 of the aperture 98 and the edge96 of the panel enters notch 95 in the bar and locks the bar againstreturn movement even when urged thereto by the trip bar return spring(not shown). The trip bar is maintained in its rotated-unlatchingposition so that subsequent attempts to reclose the circuit breaker willbe ineffective. It will be seen in FIG. 5 that the locking of theindicatoractuator bar 86 by the edge 96 of the aperture provides apositive indication as to which of the fuses has been actuated as wellas looking the circuit breaker against reclosing.

In order to render the circuit breaker operative once again, after afuse has blown, the circuit breaker is withdrawn from the cubicle (notshown) and the blown fuse, which is clearly indicated by theindicator-actuator bars, is replaced. The responder 70 is reset bymerely lifting the appropriate bar and sliding it inwardly until thenotch 86b is engaged by one of the spring 110 fingers with the bar inposition on the edge of the aperture of the front cover 14. The circuitbreaker is then returned to the cubicle and may, by appropriatemanipulation of the operating mechanism 47, be restored to its closedcircuit condition.

While only one embodiment of the invention has been shown and described,it will be understood by those skilled in the art that various changesand modifications may be made herein without departing from the spiritor scope of the invention.

What is claimed is:

1. A multi-pole circuit breaker, a plurality of currentlimiting fusesresponsive to a given magnitude of fault current, one of said fusesbeing electrically connected in series with each pole of said circuitbreaker, said multipole circuit breaker including a plurality of pairsof separable contacts each in one pole thereof and each being arrangedin series with one of said current-limiting fuses, said circuit breakerincluding a latching mechanism common to all the poles thereof, andmeans responsive to the condition of said current limiting fuses, saidresponsive means causing said latching mechanism to open said pairs ofcontacts in response to the operation of one of said fuses, saidresponsive means including means locking said latching mechanism toprevent reclosing of said circuit breaker.

2. A circuit breaker according to claim 1 further ineluding overcurrentresponsive means in each pole, said overcurrent responsive means beingoperatively related to said latching mechanism for causing separation ofsaid plurality of pairs of separable contacts upon occurrence of a faultcurrent of overload proportions of a magnitude less than said givenmagnitude.

3. A circuit breaker according to claim 1 wherein said responsive meansincludes a solenoid electrically connected in parallel with each of saidfuses, respectively, each of said solenoids having an armaturetherewith, a plurality of aligned locking members, each locking memberbeing associated with a respective one of said armatures and beingdisplaceable thereby upon operation of the associated fuse, said lockingmembers when displaced engaging said latching mechanism and locking samein a contact opening position.

4. A circuit breaker according to claim 3 wherein said circuit breakeris further provided with a front panel, each of said aligned lockingmembers having an end portion extending through an aperture in saidfront panel to the exterior thereof, said end portions being normallydisplayed therethrough in a given position and being displaced to asecond, trip indicating, position upon operation of said respective fusewhereby visual indication of operation of the fuse is given at saidfront panel.

5. A circuit breaker according to claim 4 wherein said end portions ofsaid locking members give visual indication of which fuse has operated.

References Cited UNITED STATES PATENTS 2,833,886 5/1958 Goodwin 335-463,009,037 1l/196l Jones et a1. 3377 3,309,478 3/1967 Kiesel et a1 337--7BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant ExaminerU.S. Cl. X.R. 3377, 8, 79

